My proposed studies include the following: (1) To identify the cause of the slow contraction time of muscles in patients with hypothyroidism. I plan to obtain biopsy specimens of the gastrocnemius muscle in five patients who have hypothyroidism and slow stretch reflexes. Myosin ATPase activity and rate of Ca ions uptake by the isolated sarcoplasmic reticulum will be determined and compared with the values of control muscle. (2) To test the hypothesis that sarcolemmal p-nitrophenylphosphatase activity increases in human denervation. I found that sarcolemmal p-nitrophenyl-phosphatase activity increases in denervated skeletal muscles of the rat. I plan to extend these observations to denervated human muscle. Biopsy specimens will be obtained from the muscles of patients with peripheral neuropathy, and the sarcolemmal p-nitrophenylphosphatase activity will be compared with that of human myopathic and control muscles. (3) To test the hypothesis that the ouabain-inhibited Na ion, K ion ATPase activity of the nerve in human peripheral neuropathy is related to the excitability of the nerve. I plan to measure ouabain-inhibited Na ion, K ion ATPase activity in nerve biopsy specimens from patients with different types of neuropathy in order to test the hypothesis that the activity of this enzyme is lower in axonal degenerations than in demyelinating processes. Bibliographic references: Brody, I.A. p Nitrophenylphosphatase in denervated muscle. Arch. Neurol. 31:317-319, 1974.